LongDistance Digital Connection Technologies LAN technologies cover short

Long-Distance Digital Connection Technologies ä LAN technologies cover "short" distances ä In this Chapter, we will cover: ä ä ä ä ä Digital Telephony Synchronous Communication Digital Circuits Telephone Standards Terminology and Data Rates Local Subscriber Loop ISDN, ADSL, SDSL, HDSL, VHDSL Cable Modem Technologies Hybrid Fiber Coax Fiber to the Curb 10/28/2021 1

Digital telephony ä Telephone system spans long distances ä Digital telephony improved long distance service: ä Better quality ä More connections in wire 10/28/2021 2

Digitizing voice ä ä Problem: encode analog audio signal as digital data (Digital Audio) Solution: ä Digitization: Sample audio signal periodically Conversion: Convert to digital using A-to-D converter Send Digital Audio data across network ä Reconvert to audio using D-to-A converter ä ä 10/28/2021 3

Example 10/28/2021 4

Sampling parameters ä Human voice signals up to 4000 Hz Nyquist’s theorem suggests to sample at rate > twice the highest frequency (i. e. 8000 samples/s); one sample every 125 µ sec. ä Use Pulse Code Modulation (PCM), the standard for digital encoding of audio: ä ä Samples every 125 µ sec ä Converts each sample into value in the range 0 -255 ( 8 bits) 10/28/2021 5

Synchronous communication ä Converting back to audio requires data be available "on time" ä Digital telephony systems use clocking for synchronous ä data delivery ä Samples not delayed as traffic increases 10/28/2021 6

Using digital telephony for data delivery ä So, digital telephony can handle synchronous data delivery ä Can we use that for computer data delivery? ä Ethernet frame 8 -bit PCM synchronous ä Need to convert formats. . . ä ä Use Special hardware devices called (DSU/CSU) 10/28/2021 7

Conversion for digital circuits ä ä To use digital telephony for data delivery: ä Lease point-to-point digital circuit between sites ä Convert between local and PCM formats at each end Use a Data Service Unit/Channel Service Unit (DSU/CSU) at each end ä CSU: manages control functions ä DSU: converts data 10/28/2021 8

Using DSU/CSU 10/28/2021 9

Telephone standards ä Several standards exist for data transmission rates ä Called T-series standards Name Bit Rate # Voice Circuits 0. 064 Mbps 1 T 1 1. 544 Mbps 24 T 2 6. 312 Mbps 96 # of T 1 Channels 1 T 1 (4*T 1) T 3 44. 736 Mbps 672 (28*T 1) T 4 274. 176 Mbps 4032 (168*T 1) 10/28/2021 10

Intermediate Capacity ä ä ä Price does not go up linearly with speed Cost for T 3 < cost for 28 * T 1 If all you need is 9 Mbps Cost for T 3 > Cost for 6 * T 1 Solution: combine multiple T 1 lines with inverse multiplexor 10/28/2021 11

Higher capacity circuits Synchronous Transport Signal (STS) standards refer to the high speed electrical signals used in digital transmission over copper. ä Optical Carrier (OC) standards for optical signal over fiber Standard name Optical name Bit rate Voice circuits STS-1 OC-1 51. 840 Mb 810 STS-3 OC-3 155. 520 Mbps 2, 430 STS-12 OC-12 622. 080 Mbps 9, 720 STS-24 OC-24 1, 244. 160 Mbps 19, 440 ä STS-48 10/28/2021 OC-48 2, 488. 320 Mbps 38, 880 12

About the terminology ä T-standards define underlying bit rate, Digital Signal Level standards (DS standards) define: ä ä ä how to multiplex calls effective bit rates T 1 line transmit data at DS-1 rate Synchronous Transport Signal (STS) standards define high speed connections over copper, Optical Carrier (OC) standard are for fiber C suffix indicates concatenated: ä ä OC-3 == three OC-1 circuits at 51. 84 Mbps OC-3 C == one 155. 52 Mbps circuit 10/28/2021 13

SONET ä Synchronous Optical Network (SONET) defines how to use high-speed connections ä ä ä Framing: STS-1 uses 810 bytes per frame Encoding: Each sample travels as one octet in payload Payload changes with data rate ä STS-1 transmits 6, 480 bits in 125 microseconds (== 810 octets) ä STS-3 transmits 19, 440 bits in 125 microseconds (==2, 430 octets) 10/28/2021 14

Getting to your home ä Local loop describes connection from telephone office to your home ä Sometimes called POTS (Plain Old Telephone Service) ä Legacy infrastructure is copper ä Other available connections include cable TV, wireless, electric power 10/28/2021 15

ISDN ä ä ä Provides digital service (like T-series) TP copper wiring. Basic Rate Interface (BRI) consists of three separate channels (2 B+D) : ä Two B channels (2 64 -Kbps voice circuits); ä One D channel, 16 Kbps (control) Slow to catch on ä Expensive Charge by time and distance used ä Equivalent to analog modems ä 10/28/2021 16

DSL ä DSL (Digital Subscriber Line) is a family of technologies ä ä ä One common form is ADSL (Asymmetric DSL) ä ä Sometimes called x. DSL Provides high-speed digital service over existing local loop Higher speed into home {i. e. More bits flow in ("downstream")} than out of home than out ("upstream") ADSL maximum speeds: ä 6. 144 Mbps downstream ä 640 Kbps upstream 10/28/2021 17

ADSL Technology ä Uses existing local loop copper with adaptive technology where a pair of modems probe many frequencies to select the best frequency and modulation techniques on that line to provide hi speed Use higher frequencies than used by telephones ä Does not guarantee data rate (32 kbps-6. 4 Mbps & 32 -640 Kbps) ä 10/28/2021 18

Adaptive Transmission ä Individual local loops have different transmission characteristics ä ä ä Different maximum frequencies Different interference frequencies ADSL uses FDM ä 286 frequencies ä ä 255 downstream 31 upstream 2 control Each frequency carries data independently ä ä All frequencies out of audio range Bit rate adapts to quality in each frequency 10/28/2021 19

Other DSL Technologies ä ä ä SDSL (Symmetric DSL) divides frequencies evenly HDSL (High-rate DSL) provides DS 1 bit rate both directions ä Short distances ä Four wires VDSL(Very high bit rate DSL) provides up to 52 Mbps ä Very short distance ä Requires Optical Network Unit (ONU) as a relay 10/28/2021 20

Cable Modem Technologies ä Cable TV already brings high bandwidth coax into your house ä Cable modems encode and decode data from cable TV coax ä One in cable TV center connects to network ä One in home connects to computer 10/28/2021 21

Features of Cable Modems ä Bandwidth multiplexed among all users ä Multiple access medium; your neighbor can see your data! ä Not all cable TV coax plants are bi-directional 10/28/2021 22

Upstream communication ä Cable TV is one direction ä Signal broadcast at central location ä Amplifiers boost signal through network ä Amplifiers are unidirectional! ä Solutions: ä Retrofit bi-directional amplifiers ä Alternate upstream path - e. g. , dialup 10/28/2021 23

Hybrid Fiber Coax (HFC): ä Combines ä Fiber at high capacity trunks ä Coax for feeder circuit to the individual subscribers ä Uses combination of FDM & TDM: ä 50 -450 MHz for TV (6 Mhz for each channel) ä 450 -750 MHz for downstream digital data ä 5 -50 MHz for upstream communication 10/28/2021 24

Fiber To The Curb (FTTC) ä Similar to HFC and uses: ä Fiber for high capacity trunks ä Copper for the feeder circuit to the individual subscribers ä Different from HFC: ä Uses 2 media in each feeder circuit to provide additional services such as voice 10/28/2021 25

Summary ä WAN links between sites use digital telephony ä ä Based on digitized voice service Several standard rates Requires conversion vis DSU/CSU Local loop technologies ä ISDN x. DSL Cable modem Hybrid Fiber Coax (HFC) ä Fiber to the curb (FTTC) ä ä ä 10/28/2021 26